1. Field of the Invention
The present invention relates to an image processing method and apparatus for obtaining information related to an image blur from a digital photograph image, in particular, from that obtained by the auxiliary digital camera of a mobile phone. The present invention also relates to a program that causes a computer to execute the method.
2. Description of the Related Art
Various image processing techniques are performed on digital photograph images obtained by reading devices, such as scanners, through photoelectrical reading from the photograph images recorded on camera films, such as negative films or color reversal films, or those obtained by digital still cameras (DSCs) before printing. Such image processing techniques include a blurred image restoration technique for removing blurs from blurred images.
Some of the photograph images obtained through imaging subjects may be blurred. Such a blurred image may result from the camera being out of focus at the time of imaging, which is known as the defocus blur. A blurred image may also result from the camera being shaken by the photographer at the time of imaging, which is known as the camera shake blur (or simply as “camera shake”). In the case of the defocus blur, a point image extends two-dimensionally, that is, the point images on the photograph extend nondirectionally, whereas in the case of the camera shake blur, the point image extends one-dimensionally leaving a certain trail, that is, the point images on the photograph extend to a certain direction.
Various methods for restoring blurred images have been proposed in the field of the digital photograph image. Blurred images may be restored by applying a restoration filter, such as the Wiener filter or inverted filter, if the information related to the direction and width of the camera shake at the time of imaging is available. Thus, such a restoration method is widely known as described, for example, in Japanese Unexamined Patent Publication No. 2002-112099, in which a device (e.g., acceleration sensor) capable of obtaining information related to the direction and width of the camera shake at the time of imaging is attached to the imaging system, and the information obtained through the device at the time of imaging is used for the image restoration.
Another blurred image restoration method is also known as described, for example, in Japanese Unexamined Patent Publication No. 7 (1995)-121703. The method performs the steps of setting a deterioration function for a blurred image (image having blurs), restoring the blurred image using a restoration filter corresponding to the deterioration function, evaluating the restored image, resetting the deterioration function, and repeating the steps of the image restoration, image evaluation and resetting of the deterioration function until a desirable image quality has been obtained.
In the mean time, the capability of the mobile phone has been improved along with the rapid spread of the phone. In particular, the improvement in the capability of the auxiliary digital camera of the mobile phone (mobile camera) has attracted a great deal of interest. Recently, the number of pixels of the mobile camera has reached millions digit and it is used in the same manner as an ordinary digital camera. Taking photographs of favorite entertainers, athletes, as well as commemorative photographs by mobile cameras has become a common sight. In this context, for example, more photograph images obtained by mobile cameras tend to be printed out in the same manner as those obtained by ordinary digital cameras, not just watched on the monitor of the mobile phones.
On the other hand, mobile cameras have a problem that it is difficult to hold them firmly at the time of imaging, since the body (mobile phone) is not designed for exclusive use for imaging. In addition, the mobile cameras have no photoflash, resulting in a slower shutter speeds than those of ordinary digital cameras. By the reasons described above, the camera shake blur is more likely to occur when imaging a subject with a mobile camera than with an ordinary digital camera. An extraordinary camera shake may be recognized by the photographer on the monitor of the mobile camera, but a small camera shake may not be recognized on the monitor. It is recognized only when the image is printed out, thus there is a higher likelihood that the photograph image obtained by the mobile camera requires image correction for the camera shake blur.
Attaching a device for obtaining the direction and width of the camera shake to the auxiliary camera of a mobile phone is unrealistic since the miniaturization of the mobile phone is one of the focal points of competition among the manufactures along with its capability and cost. Therefore, the method described in Japanese Unexamined Patent Publication No. 2002-112099 may not be applied for mobile cameras. Also, the method described in Japanese Unexamined Patent Publication No. 7 (1995)-121703 has a problem that it requires longer processing time, and hence inefficient, since the steps of deterioration function setting, image restoration, image evaluation, and resetting of the deterioration function need to be repeated.